Reading a Builder's Variation Breakdown — What 'Substantiation' Should Look Like (NZ)

sp8002
May 31
4 min read

You do not need to be a quantity surveyor to tell a fair variation from a padded one. You need to know what a clean breakdown contains — labour, materials, and a single margin — and the red flags that say the number was reverse-engineered.

By Steve Parker · Trueworks · NZ construction contract review · 6 min

What you'll learn

What a properly substantiated variation breakdown contains
A worked example of the shape it should take
The red flags of a padded or reverse-engineered charge

Quick answer: A properly substantiated variation shows its working: the labour hours and rate, the material cost (ideally with supplier evidence), and a single, stated margin. You are entitled to that breakdown. The red flags are round numbers with no working, a margin stacked on a provisional-sum adjustment, hours that do not match the work, and materials marked up beyond the agreed handling rate. You do not need to be a quantity surveyor to spot these — you need to know what a clean breakdown looks like.

Most homeowners feel they cannot challenge a variation because they cannot price building work. You do not have to. You only have to recognise whether the number in front of you was built up from real inputs or worked backwards from a figure the builder had in mind. The difference is visible in the breakdown.

What a clean breakdown contains

A substantiated variation has four visible parts:

Labour — the hours, and the rate per hour. Both stated, so you can see the number is hours times rate, not a guess.
Materials — the actual cost of the materials the change required, ideally with a supplier quote or invoice behind it.
Margin — a single, stated percentage or amount, applied once, at the rate your contract agreed.
Plant or subcontractor cost, where relevant — itemised, not buried.

If you can see those parts and add them up to the total, the variation is substantiated. If you cannot, it is not — yet.

A worked example (illustrative)

Here is the shape a small variation breakdown should take. The figures are illustrative, to show the structure, not market rates.

| Item | Detail | Amount | |---|---|---| | Labour | 6 hours at the contract labour rate | $510 | | Materials | Cable, socket, fittings (supplier quote attached) | $140 | | Subtotal | | $650 | | Margin | One agreed margin on the subtotal | $98 | | Variation total | | $748

The point is not the numbers. It is that every line can be checked, the margin appears once, and a supplier reference sits behind the materials.

The red flags

A round number with no working — "$1,500 for the extra works." A figure with no breakdown is the most common sign of a reverse-engineered charge.
Margin on a provisional-sum adjustment — the double-margin trap. An allowance adjustment already carries the contract margin; a second one is the line to question. (See provisional sums vs variations.)
Hours that do not match the work — a half-day job billed as two days.
Materials marked up past the agreed handling rate — materials should carry the agreed margin, not a fresh one.

"Reasonable" margin

There is no single legal margin figure in New Zealand. The margin is whatever your contract agreed — and the rule is that it is applied once, to the genuine cost. A breakdown that applies the agreed margin a single time is the test, not a particular percentage.

How to ask for substantiation

Keep it neutral and specific: "Please provide the labour hours and rate, the material costs with supplier references, and the margin applied, for variation X." A builder pricing fairly can produce this quickly. Difficulty producing it is itself informative.

Send Trueworks your contract and the line in question. You receive a written, code-cited assessment of whether it was identified, notified, and priced the way the Building Act and your contract require — a second opinion you can put straight in front of your builder. NDA available; files NZ-hosted. → Email steve@trueworks.co.nz
or start at trueworks.co.nz

Not sure a variation or charge on your build is justified?

FAQ — Reading a variation breakdown in NZ

Am I entitled to a breakdown of a variation? Yes. A variation should be substantiated — labour, materials, and the agreed margin — and you are within your rights to ask for the working before you pay.

What is a reasonable builder's margin in NZ? There is no fixed legal figure. The margin is the one your contract agreed, applied once to the genuine cost. The issue is rarely the rate; it is margin applied twice or to inflated inputs.

The variation is just a round number — is that allowed? A round number is not automatically wrong, but it is unsubstantiated until the working is shown. Ask for the breakdown.

Can the builder mark up materials? Materials carry the agreed handling margin, once. A second markup, or a rate above the agreed one, is the line to question.

What if the builder will not provide a breakdown? Difficulty substantiating a charge is informative. Put the request in writing, and if a significant figure stays unsubstantiated, get a clause-cited read before you pay.

How Trueworks helps

Trueworks reads a variation breakdown the way a quantity surveyor would — checking the labour, materials, and margin against your contract and against what the work actually required — and flags padding, double margins, and unsubstantiated lines. You get a written, code-cited account of what the variation should cost.

About Trueworks

Trueworks is built by Steve Parker — 20 years on the analytical side of NZ construction: variation reviews, contract advisory, and AI-augmented document analysis. It is the same defensible, code-cited read a quantity surveyor would give a variation, made available to the homeowners and trades on the receiving end of one. I answer every email personally during pilot phase.

steve@trueworks.co.nz · trueworks.co.nz